Large seafaring vessels are commonly powered by large internal combustion engines that require continuous cooling under various operating conditions, such as during high speed cruising, low speed operation when approaching ports, and full speed operation for avoiding bad weather, for example. Existing systems for achieving such cooling typically include one or more pumps that draw sea water into heat exchangers onboard a vessel. The heat exchangers are used to cool a closed, fresh water cooling loop that flows through and cools the engine(s) of the vessel as well as various other thermal loads onboard the vessel that require cooling (e.g., air conditioning systems).
A shortcoming associated with existing sea water cooling systems such as the one described above is that they are generally inefficient. Particularly, pumps that are employed to draw sea water into such systems are typically operated at a constant speed regardless of the amount of sea water necessary to achieve sufficient cooling of an associated engine. Thus, if an engine does not require a great deal of cooling, such as when the engine is idling or is operating at low speeds, or if the sea water being drawn into a cooling system is very cold, the pumps of the cooling system may provide more water than is necessary to achieve sufficient cooling. A portion of the energy expended to drive the pumps is therefore wasted. The pumps may be shut down to conserve energy, but will soon have to be restarted once the engine temperature rises above an acceptable limit. Of course, if the engine is still idling or is operating at low speed when the pumps are restated, or if the sea water being pumped into the system is still very cold when the pumps are restarted, the pumps will soon be shut down again once the engine temperature falls. This type of continuous on-off operation of the pumps can place a great deal of mechanical stress on the pumps as well associated system components.